The exploration of macrocycles for drug discovery — an underexploited structural class

Identification of a macrocyclic compound targeting the lassa virus polymerase

There are no approved vaccines or therapeutics for Lassa virus (LASV) infections. To identify compounds with anti-LASV activity, we conducted a cell-based screening campaign at biosafety level 4 and tested almost 60,000 compounds for activity against an infectious reporter LASV. Hits from this screen included several structurally related macrocycles. The most potent, Mac128, had a sub-micromolar EC50 against the reporter virus, inhibited wild-type clade IV LASV, and reduced viral titers by 4 orders of magnitude. Mechanistic studies suggested that Mac128 inhibited viral replication at the level of the polymerase.

Discovery of MK-1084: An Orally Bioavailable and Low-Dose KRASG12C Inhibitor

Oncogenic mutations in the RAS gene account for 30% of all human tumors; more than 60% of which present as KRAS mutations at the hotspot codon 12. After decades of intense pursuit, a covalent inhibition strategy has enabled selective targeting of this previously "undruggable" target. Herein, we disclose our journey toward the discovery of MK-1084, an orally bioavailable and low-dose KRASG12C covalent inhibitor currently in phase I clinical trials (NCT05067283). We leveraged structure-based drug design to identify a macrocyclic core structure, and hypothesis-driven optimization of biopharmaceutical properties to further improve metabolic stability and tolerability.

Stereochemical Assignment of the 36-Membered Macrolide Ring Portion of Poecillastrin C

Absolute configuration at 12 stereocenters in the 36-membered macrocyclic ring portion of poecillastrin C (1) was disclosed by chemical degradation and NMR analyses of 1, chemical synthesis, and molecular modeling techniques.

Production of constrained L-cyclo-tetrapeptides by epimerization-resistant direct aminolysis

The synthesis of constrained 12-membered rings is notably difficult. The main challenges result from constraints during the linear peptide cyclization. Attempts to overcome constraints through excessive activation frequently cause peptidyl epimerization, while insufficient activation of the C-terminus hampers cyclization and promotes intermolecular oligomer formation. We present a β-thiolactone framework that enables the synthesis of cyclo-tetrapeptides via direct aminolysis. This tactic utilizes a mechanism that restricts C-terminal carbonyl rotation while maintaining high reactivity, thereby enabling efficient head-to-tail amidation, reducing oligomerization, and preventing epimerization. A broad range of challenging cyclo-tetrapeptides ( > 20 examples) are synthesized in buffer and exhibits excellent tolerance toward nearly all proteinogenic amino acids. Previously unattainable macrocycles, such as cyclo-L-(Pro-Tyr-Pro-Val), have been produced and identified as μ-opioid receptor (MOR) agonists, with an EC50 value of 2.5 nM. Non-epimerizable direct aminolysis offers a practical solution for constrained peptide cyclization, and the discovery of MOR agonist activity highlights the importance of overcoming synthetic challenges for therapeutic development.

Large Libraries of Structurally Diverse Macrocycles Suitable for Membrane Permeation

Macrocycles offer an attractive format for drug development due to their good binding properties and potential to cross cell membranes. To efficiently identify macrocyclic ligands for new targets, methods for the synthesis and screening of large combinatorial libraries of small cyclic peptides were developed, many of them using thiol groups for efficient peptide macrocyclization. However, a weakness of these libraries is that invariant thiol-containing building blocks such as cysteine are used, resulting in a region that does not contribute to library diversity but increases molecule size. Herein, we synthesized a series of structurally diverse thiol-containing elements and used them for the combinatorial synthesis of a 2,688-member library of small, structurally diverse peptidic macrocycles with unprecedented skeletal complexity. We then used this library to discover potent thrombin and plasma kallikrein inhibitors, some also demonstrating favorable membrane permeability. X-ray structure analysis of macrocycle-target complexes showed that the size and shape of the newly developed thiol elements are key for binding. The strategy and library format presented in this work significantly enhance structural diversity by allowing combinatorial modifications to a previously invariant region of peptide macrocycles, which may be broadly applied in the development of membrane permeable therapeutics.

Electrochemical synthesis of peptide aldehydes via C‒N bond cleavage of cyclic amines

Peptide aldehydes are crucial biomolecules essential to various biological systems, driving a continuous demand for efficient synthesis methods. Herein, we develop a metal-free, facile, and biocompatible strategy for direct electrochemical synthesis of unnatural peptide aldehydes. This electro-oxidative approach enabled a step- and atom-economical ring-opening via C‒N bond cleavage, allowing for homoproline-specific peptide diversification and expansion of substrate scope to include amides, esters, and cyclic amines of various sizes. The remarkable efficacy of the electro-synthetic protocol set the stage for the efficient modification and assembly of linear and macrocyclic peptides using a concise synthetic sequence with racemization-free conditions. Moreover, the combination of experiments and density functional theory (DFT) calculations indicates that different N-acyl groups play a decisive role in the reaction activity.

Destruxin E backbone modification effects on osteoclast Morphology: Synthesis and SAR study of N-Desmethyl and N-Methyl analogs

The design and synthesis of N-desmethyl and N-methyl destruxin E analogs have been demonstrated. The X-ray single crystal structure of destruxin E (1a) revealed a stable three-dimensional (3D) structure, including a s-cis amide bond at the MeVal-MeAla moiety and two intramolecular hydrogen bonds between NH(β-Ala) and OC(Ile) and between NH(Ile) and OC(β-Ala). N-Desmethyl analogs 2a (MeAla → Ala) and 2b (MeVal → Val) were synthesized through macrolactonization similar to our previously reported synthesis of 1a. Conversely, for the synthesis of N-methyl analogs 2c (Ile → MeIle) and 2d (β-Ala → Meβ-Ala), macrolactonization did not proceed; therefore, cyclization precursors 10c and 10d were designed to maintain the intramolecular hydrogen bonds described above during their cyclization. The macrolactamization proceeded despite the presence of a less reactive N-methylamino group at the N-terminus in both cases. Analog 2a, which exhibits multiple conformers in solutions, was inactive at 50 μM, whereas analog 2b, which exhibits a conformation similar to that of 1a in solutions, exhibited morphological changes against osteoclast-like multinuclear cells at 1.6 μM. The activity of the MeIle analog 2c, which cannot take the intramolecular hydrogen bond (Ile)NH•••OC(β-Ala) in 1a, was markedly diminished compared with that of 1a, and that of the Meβ-Ala analog 2d, which cannot take the intramolecular hydrogen bond (β-Ala)NH•••OC(Ile) in 1a, was further reduced to one-fourth of that of 2c. The overall results indicate that both the s-cis amide bond at the MeVal-MeAla moiety and two intramolecular hydrogen bonds (β-Ala)NH•••OC(Ile) and (Ile)NH•••OC(β-Ala) are important for constraining the conformation of the macrocyclic peptide backbone in destruxin E, thereby exhibiting its potent biological activity.

Structure-Based Rational Design of Constrained Peptides as TIM-3 Inhibitors

Blocking the immunosuppressive function of T-cell immunoglobulin mucin-3 (TIM-3) is an established therapeutic strategy to maximize the efficacy of immune checkpoint inhibitors for cancer immunotherapy. Currently, effective inhibition of TIM-3 interactions relies on monoclonal antibodies (mAbs), which come with drawbacks such as immunogenicity risk, limited tumor penetration, and high manufacturing costs. Guided by the X-ray cocrystal structures of TIM-3 with mAbs, we report an in silico structure-based rational design of constrained peptides as potent TIM-3 inhibitors. The top cyclic peptide from our study (P2) binds TIM-3 with a K D value of 166.3 ± 12.1 nM as determined by surface plasmon resonance (SPR) screening. Remarkably, P2 efficiently inhibits key TIM-3 interactions with natural TIM-3 ligands at submicromolar concentrations in a panel of cell-free and cell-based assays. The capacity of P2 to reverse immunosuppression in T-cell/cancer cell cocultures, coupled with favorable in vitro pharmacokinetic properties, highlights the potential of P2 for further evaluation in preclinical models of immuno-oncology.

Macrocyclization strategy for improving candidate profiles in medicinal chemistry

Macrocycles are defined as cyclic compounds with 12 or more members. In medicinal chemistry, they are categorized based on their core chemistry into cyclic peptides and macrocycles. Macrocycles are advantageous because of their structural diversity and ability to achieve high affinity and selectivity towards challenging targets that are often not addressable by conventional small molecules. The potential of macrocyclization to optimize drug-like properties while maintaining adequate bioavailability and permeability has been emphasized as a key innovation in medicinal chemistry. This review provides a detailed case study of the application of macrocyclization over the past 5 years, starting from the initial analysis of acyclic active compounds to optimization of the resulting macrocycles for improved efficacy and drug-like properties. Additionally, it illustrates the strategic value of macrocyclization in contemporary drug discovery efforts.

An Amphiphilic Cell-Penetrating Macrocycle for Efficient Cytosolic Delivery of Proteins, DNA, and CRISPR Cas9

The discovery of safe platforms that can circumvent the endocytic pathway is of great significance for biological therapeutics that are usually degraded during endocytosis. Here we show that a self-assembled and dynamic macrocycle can passively diffuse through the cell membrane and deliver a broad range of biologics, including proteins, CRISPR Cas9, and ssDNA, directly to the cytosol while retaining their bioactivity. Cell-penetrating macrocycle CPM can be easily prepared from the room temperature condensation of diketopyrrolopyrrole lactams with diamines. We attribute the high cellular permeability of CPM to its amphiphilic nature and chameleonic properties. It adopts conformations that partially bury polar groups and expose hydrophobic side chains, thus self-assembling into micellar-like structures. Its superior fluorescence makes CPM trackable inside cells where it follows the endomembrane system. CPM outperformed commercial reagents for biologics delivery and showed high RNA knockdown efficiency of CRISPR Cas9. We envisage that this macrocycle will be an ideal starting point to design and synthesize biomimetic macrocyclic tags that can readily facilitate the interaction and uptake of biomolecules and overcome endosomal digestion.

Cascade ring expansion reactions for the synthesis of medium-sized rings and macrocycles

This Feature Article discusses recent advances in the development of cascade ring expansion reactions for the synthesis of medium-sized rings and macrocycles. Cascade ring expansion reactions have much potential for use in the synthesis of biologically important medium-sized rings and macrocycles, most notably as they don't require high dilution conditions, which are commonly used in established end-to-end macrocyclisation methods. Operation by cascade ring expansion method can allow large ring products to be accessed via rearrangements that proceed exclusively by normal-sized ring cyclisation steps. Ensuring that there is adequate thermodynamic driving force for ring expansion is a key challenge when designing such methods, especially for the expansion of normal-sized rings into medium-sized rings. This Article is predominantly focused on methods developed in our own laboratory, with selected works by other groups also discussed. Thermodynamic considerations, mechanism, reaction design, route planning and future perspective for this field are all covered.

New Polyether Macrocycles as Promising Antitumor Agents-Targeted Synthesis and Induction of Mitochondrial Apoptosis

A series of previously unknown aromatic polyether macrodiolides containing a cis,cis-1,5-diene moiety in the molecule were synthesized in 47-74% yields. Macrocycle compounds were first obtained by intermolecular esterification of aromatic polyether diols with α,ω-alka-nZ,(n+4)Z-dienedioic acids mediated by N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC·HCl) and 4-(dimethylamino)pyridine (DMAP). For the synthesized compounds, studies of cytotoxicity on tumor (Jurkat, K562, U937), conditionally normal (HEK293) cell lines, and normal fibroblasts were carried out. CC50 was determined, and the therapeutic selectivity index of cytotoxic action (SI) in comparison with normal fibroblasts was evaluated. With the involvement of modern methods of flow cytometry for the most promising macrocycles, their effect on mitochondria and the cell cycle was investigated. It was found that a new macrocycle exhibits pronounced apoptosis-inducing activity toward Jurkat cells and can retard cell division by blocking at the G1/S checkpoint. Also, it was shown that the synthesized macrodiolides influence mitochondria due to their high ability to penetrate the mitochondrial membrane.

In2Q2: A New Entry of 16-Membered Tetraazamacrocycle Concatenating Indole and Quinoline Units

A new family of 16-membered macrocycles comprising two indole (In) and two quinoline (Q) units, coined In2Q2, was synthesized. Each unit is diagonally located and concatenated in a head-to-tail fashion, furnishing a non-flat saddle-shaped architecture with C2 symmetry. The synthetic protocol utilizing macrocyclic diamide as a pivotal precursor allowed us to access a series of In2Q2 derivatives bearing various substituents on the periphery. The In2Q2 derivatives and their Zn2+ complexes were emissive in both solution phase and solid state. While the entire architecture of In2Q2 is similar to that of quinoline tetramer TEtraQuinoline, a couple of contrasting physicochemical properties were revealed.

Continuous Synthesis of a Macrocyclic Sulfite of Polyethylene Glycol by Cascaded Continuous Stirred Tank Reactors (CSTRs)

Many macrocyclic compounds are attractive drug-like molecules or intermediates due to their special properties. However, the bulk synthesis of such compounds are hindered by the necessity of using diluted solutions, in order to prevent intermolecular reactions that yields oligomer impurities, thereby resulting in a low production efficiency. Such challenge can be adequately addressed by using continuous reactors, allowing improved efficiency with smaller space footprints. In this work, we proposed a novel continuous process for the synthesis of a macrocyclic sulfite of tetraethylene glycol (PEG4-MCSi), which is a precursor to a very useful building block, PEG4-macrocyclic sulfate (PEG4-MCS). The basic reaction parameters, including stoichiometry and temperature, were first confirmed with small batch reactions, and the effectiveness of coiled reactors and continuous stirred tank reactors (CSTRs) were compared. Cascaded CSTRs were proven to be suitable, and the reaction parameters were subject to further optimization to give a robust continuous process. The process was then tested with 4 parallel runs for up to 64 h. Finally, the merits and demerits of batch and continuous reactions were also compared, demonstrating the suitability of latter in the bulk production of macrocyclic PEG-MCSi compounds.

The macrocycle inhibitor landscape of SLC-transporter

In the past years the interest in Solute Carrier Transporters (SLC) has increased due to their potential as drug targets. At the same time, macrocycles demonstrated promising activities as therapeutic agents. However, the overall macrocycle/SLC-transporter interaction landscape has not been fully revealed yet. In this study, we present a statistical analysis of macrocycles with measured activity against SLC-transporter. Using a data mining pipeline based on KNIME retrieved in total 825 bioactivity data points of macrocycles interacting with SLC-transporter. For further analysis of the SLC inhibitor profiles we developed an interactive KNIME workflow as well as an interactive map of the chemical space coverage utilizing parametric t-SNE models. The parametric t-SNE models provide a good discrimination ability among several corresponding SLC subfamilies' targets. The KNIME workflow, the dataset, and the visualization tool are freely available to the community.

Polymorphic Structure Determination of the Macrocyclic Drug Paritaprevir by MicroED

Paritaprevir is an orally bioavailable, macrocyclic drug used for treating chronic Hepatitis C virus (HCV) infection. Its structures have been elusive to the public until recently when one of the crystal forms is solved by microcrystal electron diffraction (MicroED). In this work, the MicroED structures of two distinct polymorphic crystal forms of paritaprevir are reported from the same experiment. The different polymorphs show conformational changes in the macrocyclic core, as well as the cyclopropyl sulfonamide and methyl pyrazinamide substituents. Molecular docking shows that one of the conformations fits well into the active site pocket of the HCV non-structural 3/4A (NS3/4A) serine protease target, and can interact with the pocket and catalytic triad via hydrophobic interactions and hydrogen bonds. These results can provide further insight for optimization of the binding of acyl sulfonamide inhibitors to the HCV NS3/4A serine protease. In addition, this also demonstrates the opportunity to derive different polymorphs and distinct macrocycle conformations from the same experiments using MicroED.

Discovery of a nitroaromatic nannocystin with potent in vivo anticancer activity against colorectal cancer by targeting AKT1

The development of targeted chemotherapeutic agents against colorectal cancer (CRC), one of the most common cancers with a high mortality rate, is in a constant need. Nannocystins are a family of myxobacterial secondary metabolites featuring a 21-membered depsipeptide ring. The in vitro anti-CRC activity of natural and synthetic nannocystins was well documented, but little is known about their in vivo efficacy and if positive, the underlying mechanism of action. In this study we synthesized a nitroaromatic nannocystin through improved preparation of a key fragment, and characterized its in vitro activity and in vivo efficacy against CRC. We first described the total synthesis of compounds 2-4 featuring Heck macrocyclization to forge their 21-membered macrocycle. In a panel of 7 cancer cell lines from different tissues, compound 4 inhibited the cell viability with IC values of 1-6 nM. In particular, compound 4 (1, 2, 4 nM) inhibited the proliferation of CRC cell lines (HCT8, HCT116 and LoVo) in both concentration and time dependent manners. Furthermore, compound 4 concentration-dependently inhibited the colony formation and migration of CRC cell lines. Moreover, compound 4 induced cell cycle arrest at sub-G1 phase, apoptosis and cellular senescence in CRC cell lines. In three patient-derived CRC organoids, compound 4 inhibited the PDO with IC values of 3.68, 28.93 and 11.81 nM, respectively. In a patient-derived xenograft mouse model, injection of compound 4 (4, 8 mg/kg, i.p.) every other day for 12 times dose-dependently inhibited the tumor growth without significant change in body weight. We conducted RNA-sequencing, molecular docking and cellular thermal shift assay to elucidate the anti-CRC mechanisms of compound 4, and revealed that it exerted its anti-CRC effect at least in part by targeting AKT1.

Expansive discovery of chemically diverse structured macrocyclic oligoamides

Small macrocycles with four or fewer amino acids are among the most potent natural products known, but there is currently no way to systematically generate such compounds. We describe a computational method for identifying ordered macrocycles composed of alpha, beta, gamma, and 17 other amino acid backbone chemistries, which we used to predict 14.9 million closed cycles composed of >42,000 monomer combinations. We chemically synthesized 18 macrocycles predicted to adopt single low-energy states and determined their x-ray or nuclear magnetic resonance structures; 15 of these were very close to the design models. We illustrate the therapeutic potential of these macrocycle designs by developing selective inhibitors of three protein targets of current interest. By opening up a vast space of readily synthesizable drug-like macrocycles, our results should considerably enhance structure-based drug design.

Design and Synthesis of Novel Macrocyclic Derivatives as Potent and Selective Cyclin-Dependent Kinase 7 Inhibitors

The duality of function (cell cycle regulation and gene transcription) of cyclin-dependent kinase 7 (CDK7) makes it an attractive oncology target and the discovery of CDK7 inhibitors has been a long-term pursuit by academia and pharmaceutical companies. However, achieving selective leading compounds is still difficult owing to the similarities among the ATP binding pocket. Herein, we detail the design and synthesis of a series of macrocyclic derivatives with pyrazolo[1,5-a]-1,3,5-triazine core structure as potent and selective CDK7 inhibitors. The diverse manners of macrocyclization led to distinguished selectivity profiles of the CDK family. Molecular dynamics (MD) simulation explained the binding difference between 15- and 16-membered macrocyclic compounds. Further optimization generated compound 37 exhibiting good CDK7 inhibitory activity and high selectivity over other CDKs. This work clearly demonstrated macrocyclization is a versatile method to finely tune the selectivity profile of small molecules and MD simulation can be a valuable tool in prioritizing designs of the macrocycle.

Macrocyclic Dual-Locked "Turn-On" Drug for Selective and Traceless Release in Cancer Cells

Drug safety and efficacy due to premature release into the bloodstream and poor biodistribution remains a problem despite seminal advances in this area. To circumvent these limitations, we report drug cyclization based on dynamic covalent linkages to devise a dual lock for the small-molecule anticancer drug, camptothecin (CPT). Drug activity is "locked" within the cyclic structure by the redox responsive disulfide and pH-responsive boronic acid-salicylhydroxamate and turns on only in the presence of acidic pH, reactive oxygen species and glutathione through traceless release. Notably, the dual-responsive CPT is more active (100-fold) than the non-cleavable (permanently closed) analogue. We further include a bioorthogonal handle in the backbone for functionalization to generate cyclic-locked, cell-targeting peptide- and protein-CPTs, for targeted delivery of the drug and traceless release in triple negative metastatic breast cancer cells to inhibit cell growth at low nanomolar concentrations.

Taming Conformational Heterogeneity on Ion Racetrack to Unveil Principles that Drive Membrane Permeation of Cyclosporines

Our study reveals the underlying principles governing the passive membrane permeability in three large N-methylated macrocyclic peptides (N-MeMPs): cyclosporine A (CycA), Alisporivir (ALI), and cyclosporine H (CycH). We determine a series of conformers required for robust passive membrane diffusion and those relevant to other functions, such as binding to protein targets or intermediates, in the presence of solvent additives. We investigate the conformational interconversions and establish correlations with the membrane permeability. Nuclear magnetic resonance (NMR) and cyclic ion-mobility spectrometry-mass spectrometry (cIMS-MS) are employed to characterize conformational heterogeneity and identify cis-amides relevant for good membrane permeability. In addition, ion mobility selected cIMS-MS and infrared (IR) multiple-photon dissociation (IRMPD) spectroscopy experiments are conducted to evaluate the energy barriers between conformations. We observe that CycA and ALI, both cyclosporines with favorable membrane permeabilities, display multiple stable and well-defined conformers. In contrast, CycH, an epimer of CycA with limited permeability, exhibits fewer and fewer stable conformers. We demonstrate the essential role of the conformational shift from the aqueous cis MeVal11-MeBmt1 state (A1) to the closed conformation featuring cis MeLeu9-MeLeu10 (C1) in facilitating membrane permeation. Additionally, we highlight that the transition from A1 to the all-trans open conformation (O1) is specifically triggered by the presence of CaCl2. We also capture a set of conformers with cis Sar3-MeLeu4, MeLeu9-MeLeu10, denoted as I. Conformationally selected cIMS-MS and IRMPD data of [CycA+Ca]2+ show immediate repopulation of the original population distribution, suggesting that CaCl2 smooths out the energy barriers. Finally, our work presents an improved sampling molecular dynamics approach based on a refined force field that not only consistently and accurately captures established conformers of cyclosporines but also exhibits strong predictive capabilities for novel conformers.

Anti-Neuroinflammatory Effects of a Macrocyclic Peptide-Peptoid Hybrid in Lipopolysaccharide-Stimulated BV2 Microglial Cells

Inflammation processes of the central nervous system (CNS) play a vital role in the pathogenesis of several neurological and psychiatric disorders like depression. These processes are characterized by the activation of glia cells, such as microglia. Clinical studies showed a decrease in symptoms associated with the mentioned diseases after the treatment with anti-inflammatory drugs. Therefore, the investigation of novel anti-inflammatory drugs could hold substantial potential in the treatment of disorders with a neuroinflammatory background. In this in vitro study, we report the anti-inflammatory effects of a novel hexacyclic peptide-peptoid hybrid in lipopolysaccharide (LPS)-stimulated BV2 microglial cells. The macrocyclic compound X15856 significantly suppressed Interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), c-c motif chemokine ligand 2 (CCL2), CCL3, C-X-C motif chemokine ligand 2 (CXCL2), and CXCL10 expression and release in LPS-treated BV2 microglial cells. The anti-inflammatory effects of the compound are partially explained by the modulation of the phosphorylation of p38 mitogen-activated protein kinases (MAPK), p42/44 MAPK (ERK 1/2), protein kinase C (PKC), and the nuclear factor (NF)-κB, respectively. Due to its remarkable anti-inflammatory properties, this compound emerges as an encouraging option for additional research and potential utilization in disorders influenced by inflammation, such as depression.

Expanding the scope of the successive ring expansion strategy for macrocycle and medium-sized ring synthesis: unreactive and reactive lactams

New methods are described that expand the scope of the Successive Ring Expansion (SuRE) with respect to synthetically challenging lactams. A protocol has been developed for use with 'unreactive' lactams, enabling SuRE reactions to be performed on subsrates that fail under previously established conditions. Ring expansion is also demonstarted on 'reactive' lactams derived from iminosugars for the first time. The new SuRE methods were used to prepare a diverse array of medium-sized and macrocyclic lactams and lactones, which were evaluted in an anti-bacterial assay against E. coli BW25113WT.

The Inhibition of NS2B/NS3 Protease: A New Therapeutic Opportunity to Treat Dengue and Zika Virus Infection

In the global pandemic scenario, dengue and zika viruses (DENV and ZIKV, respectively), both mosquito-borne members of the flaviviridae family, represent a serious health problem, and considering the absence of specific antiviral drugs and available vaccines, there is a dire need to identify new targets to treat these types of viral infections. Within this drug discovery process, the protease NS2B/NS3 is considered the primary target for the development of novel anti-flavivirus drugs. The NS2B/NS3 is a serine protease that has a dual function both in the viral replication process and in the elusion of the innate immunity. To date, two main classes of NS2B/NS3 of DENV and ZIKV protease inhibitors have been discovered: those that bind to the orthosteric site and those that act at the allosteric site. Therefore, this perspective article aims to discuss the main features of the use of the most potent NS2B/NS3 inhibitors and their impact at the social level.

Asparaginyl Endopeptidase-Mediated Peptide Cyclization for Phage Display

We report here an enzymatic strategy for asparaginyl endopeptidase-mediated peptide cyclization. Incorporation of chloroacetyl groups into the recognition sequence of OaAEP1 enabled intramolecular cyclization with Cys residues. Combining this strategy and phage display, we identified nanomolar macrocyclic peptide ligands targeting TEAD4. One of the bicyclic peptides binds to TEAD4 with a KD value of 139 nM, 16 times lower than its linear analogue, demonstrating the utility of this platform in discovering high-affinity macrocyclic peptide ligands.

CyclicPepedia: a knowledge base of natural and synthetic cyclic peptides

Cyclic peptides offer a range of notable advantages, including potent antibacterial properties, high binding affinity and specificity to target molecules, and minimal toxicity, making them highly promising candidates for drug development. However, a comprehensive database that consolidates both synthetically derived and naturally occurring cyclic peptides is conspicuously absent. To address this void, we introduce CyclicPepedia (https://www.biosino.org/iMAC/cyclicpepedia/), a pioneering database that encompasses 8744 known cyclic peptides. This repository, structured as a composite knowledge network, offers a wealth of information encompassing various aspects of cyclic peptides, such as cyclic peptides' sources, categorizations, structural characteristics, pharmacokinetic profiles, physicochemical properties, patented drug applications, and a collection of crucial publications. Supported by a user-friendly knowledge retrieval system and calculation tools specifically designed for cyclic peptides, CyclicPepedia will be able to facilitate advancements in cyclic peptide drug development.

Targeted sampling of natural product space to identify bioactive natural product-like polyketide macrolides

Polyketide or polyketide-like macrolides (pMLs) continue to serve as a source of inspiration for drug discovery. However, their inherent structural and stereochemical complexity challenges efforts to explore related regions of chemical space more broadly. Here, we report a strategy termed the Targeted Sampling of Natural Product space (TSNaP) that is designed to identify and assess regions of chemical space bounded by this important class of molecules. Using TSNaP, a family of tetrahydrofuran-containing pMLs are computationally assembled from pML inspired building blocks to provide a large collection of natural product-like virtual pMLs. By scoring functional group and volumetric overlap against their natural counterparts, a collection of compounds are prioritized for targeted synthesis. Using a modular and stereoselective synthetic approach, a library of polyketide-like macrolides are prepared to sample these unpopulated regions of pML chemical space. Validation of this TSNaP approach by screening this library against a panel of whole-cell biological assays, reveals hit rates exceeding those typically encountered in small molecule libraries. This study suggests that the TSNaP approach may be more broadly useful for the design of improved chemical libraries for drug discovery.

Total Synthesis and Determination of the Absolute Configuration of Berkeleylactone I

Herein, we report the first total synthesis of berkeleylactone I and its 12S diastereomer. Consequently, this chemical synthesis allowed us to establish the unknown absolute stereochemistry at the C-12 center as 12R, which was unidentified by the isolation group. This synthetic approach includes several critical reactions, such as the Sharpless asymmetric dihydroxylation, Baran's Ni-catalyzed alkyl-alkyl cross-coupling reaction, Brown allylation, Mitsunobu reaction, and ring-closing metathesis, as key steps.

N-Heterocyclic carbene-catalyzed enantioselective synthesis of planar-chiral cyclophanes via dynamic kinetic resolution

Planar-chiral cyclophanes have gained considerable concerns for drug discovery due to their unique conformational strain and 3D structure. However, the enantioselective synthesis of planar-chiral cyclophanes is a long-standing challenge for the synthetic community. We herein describe an N-heterocyclic carbene (NHC)-catalyzed asymmetric construction of planar-chiral cyclophanes. This transformation occurs through a dynamic kinetic resolution (DKR) process to convert racemic substrates into planar-chiral macrocycle scaffolds in good to high yields with high to excellent enantioselectivities. The ansa chain length and aromatic ring substituent size is crucial to achieve the DKR approach. Controlled experiments and DFT calculations were performed to clarify the DKR process.

Insights on Structure-Passive Permeability Relationship in Pyrrole and Furan-Containing Macrocycles

Macrocycles have recognized therapeutic potential, but their limited cellular permeability can hinder their development as oral drugs. To better understand the structure-permeability relationship of heterocycle-containing, semipeptidic macrocycles, a library was synthesized. These compounds were created by developing two novel reactions described herein: the reduction of activated oximes by LiBH4 and the aqueous reductive mono-N-alkylation of aldehydes using catalytic SmI2 and stoichiometric Zn. The permeability of the macrocycles was evaluated through a parallel artificial membrane permeability assay (PAMPA), and the results indicated that macrocycles with a furan incorporated into the structure have better passive permeability than those with a pyrrole moiety. Compounds bearing a 2,5-disubstituted pyrrole (endo orientation) were shown to be implicated in intramolecular H-bonds, enhancing their permeability. This study highlighted the impact of heterocycles moieties in semipeptides, creating highly permeable macrocycles, thus showing promising avenues for passive diffusion of drugs beyond the rule-of-five chemical space.

Systematic analysis, aggregation and visualisation of interaction fingerprints for molecular dynamics simulation data

Computational methods such as molecular docking or molecular dynamics (MD) simulations have been developed to simulate and explore the interactions between biomolecules. However, the interactions obtained using these methods are difficult to analyse and evaluate. Interaction fingerprints (IFPs) have been proposed to derive interactions from static 3D coordinates and transform them into 1D bit vectors. More recently, the concept has been applied to derive IFPs from MD simulations, which adds a layer of complexity by adding the temporal motion and dynamics of a system. As a result, many IFPs are obtained from one MD simulation, resulting in a large number of individual IFPs that are difficult to analyse compared to IFPs derived from static 3D structures. Scientific contribution: We introduce a new method to systematically aggregate IFPs derived from MD simulation data. In addition, we propose visualisations to effectively analyse and compare IFPs derived from MD simulation data to account for the temporal evolution of interactions and to compare IFPs across different MD simulations. This has been implemented as a freely available Python library and can therefore be easily adopted by other researchers and to different MD simulation datasets.

Rapid, traceless and facile peptide cyclization enabled by tetrazine-thiol exchange

Cyclic peptides offer many advantages compared to their linear counterparts, including prolonged stability within the biological environment and enhanced binding affinity. Typically, peptides are cyclized by forming an amide bond, either on-resin or in solution, through extensive use of orthogonal protecting groups or chemoselective ligation strategies, respectively. Here, we show that the chemoselective tetrazine-thiol exchange is a powerful tool for rapid in situ cyclization of peptides without the need for additional activation reagents or extensive protecting group reshuffling. The reaction between N-terminal sulfide-bearing unsymmetric tetrazines and internal cysteines occurs spontaneously within a mildly acidic environment (pH 6.5) and is of traceless nature. The rapidly available unsymmetric sulfide tetrazine building blocks can be incorporated on resin using standard solid-phase peptide synthesis protocols and are orthogonal to trifluoroacetic acid cleavage conditions. The cyclized peptides display high stability, even when incubated with a large excess of free thiols. Due to its traceless and mild nature, we expect that the tetrazine-thiol exchange will be of high value for the in situ formation of cyclic peptide libraries, thus being applicable in drug discovery and development.

A Modular Strategy for the Synthesis of Macrocycles and Medium-Sized Rings via Cyclization/Ring Expansion Cascade Reactions

Macrocycles and medium-sized rings are important in many scientific fields and technologies but are hard to make using current methods, especially on a large scale. Outlined herein is a strategy by which functionalized macrocycles and medium-sized rings can be prepared using cyclization/ring expansion (CRE) cascade reactions, without resorting to high dilution conditions. CRE cascade reactions are designed to operate exclusively via kinetically favorable 5-7-membered ring cyclization steps; this means that the problems typically associated with classical end-to-end macrocyclization reactions are avoided. A modular synthetic approach has been developed to facilitate the simple assembly of the requisite linear precursors, which can then be converted into an extremely broad range of functionalized macrocycles and medium-sized rings using one of nine CRE protocols.

Kinase inhibitor macrocycles: a perspective on limiting conformational flexibility when targeting the kinome with small molecules

Methods utilized for drug discovery and development within the kinome have rapidly evolved since the approval of imatinib, the first small molecule kinase inhibitor. Macrocycles have received increasing interest as a technique to improve kinase inhibitor drug properties evident by the FDA approvals of lorlatinib, pacritinib, and repotrectinib. Compared to their acyclic counterparts, macrocycles can possess improved pharmacodynamic and pharmacokinetic properties. This review highlights clinical success stories when implementing macrocycles in kinase-based drug discovery and showcases that macrocyclization is a clinically validated drug discovery strategy when targeting the kinome.

Multi_CycGT: A Deep Learning-Based Multimodal Model for Predicting the Membrane Permeability of Cyclic Peptides

Cyclic peptides are gaining attention for their strong binding affinity, low toxicity, and ability to target "undruggable" proteins; however, their therapeutic potential against intracellular targets is constrained by their limited membrane permeability, and researchers need much time and money to test this property in the laboratory. Herein, we propose an innovative multimodal model called Multi_CycGT, which combines a graph convolutional network (GCN) and a transformer to extract one- and two-dimensional features for predicting cyclic peptide permeability. The extensive benchmarking experiments show that our Multi_CycGT model can attain state-of-the-art performance, with an average accuracy of 0.8206 and an area under the curve of 0.8650, and demonstrates satisfactory generalization ability on several external data sets. To the best of our knowledge, it is the first deep learning-based attempt to predict the membrane permeability of cyclic peptides, which is beneficial in accelerating the design of cyclic peptide active drugs in medicinal chemistry and chemical biology applications.

Divergent Cascade Ring-Expansion Reactions of Acryloyl Imides

Macrocyclic and medium-sized ring ketones, lactones and lactams can all be made from common acryloyl imide starting materials through divergent, one-pot cascade ring-expansion reactions. Following either conjugate addition with an amine or nitromethane, or osmium(VIII)-catalysed dihydoxylation, rearrangement through a four-atom ring expansion takes place spontaneously to form the ring expanded products. A second ring expansion can also be performed following a second iteration of imide formation and alkene functionalisation/ring expansion. In the dihydroxylation series, three- or four-atom ring expansion can be performed selectively, depending on whether the reaction is under kinetic or thermodynamic control.

Design of cyclic peptides as novel inhibitors of ICOS/ICOSL interaction

Compared to small molecules and antibodies, cyclic peptides exhibit unique biochemical and therapeutic attributes in the realm of pharmaceutical applications. The interaction between the inducible costimulator (ICOS) and its ligand (ICOSL) plays a key role in T-cell differentiation and activation. ICOS/ICOSL inhibition results in a reduction in the promotion of immunosuppressive regulatory T cells (Tregs) in both hematologic malignancies and solid tumors. Herein, we implement the computational cPEPmatch approach to design the first examples of cyclic peptides that inhibit ICOS/ICOSL interaction. The top cyclic peptide from our approach possessed an IC50 value of 1.87 ± 0.15 μM as an ICOS/ICOSL inhibitor and exhibited excellent in vitro pharmacokinetic properties as a drug candidate. Our work will lay the groundwork for future endeavors in cancer drug discovery, with the goal of developing cyclic peptides that target the ICOS/ICOSL interaction.

The Genus Cladosporium: A Prospective Producer of Natural Products

Cladosporium, a genus of ascomycete fungi in the Dematiaceae family, is primarily recognized as a widespread environmental saprotrophic fungus or plant endophyte. Further research has shown that the genus is distributed in various environments, particularly in marine ecosystems, such as coral reefs, mangroves and the polar region. Cladosporium, especially the marine-derived Cladosporium, is a highly resourceful group of fungi whose natural products have garnered attention due to their diverse chemical structures and biological activities, as well as their potential as sources of novel leads to compounds for drug production. This review covers the sources, distribution, bioactivities, biosynthesis and structural characteristics of compounds isolated from Cladosporium in the period between January 2000 and December 2022, and conducts a comparative analysis of the Cladosporium isolated compounds derived from marine and terrestrial sources. Our results reveal that 34% of Cladosporium-derived natural products are reported for the first time. And 71.79% of the first reported compounds were isolated from marine-derived Cladosporium. Cladosporium-derived compounds exhibit diverse skeletal chemical structures, concentrating in the categories of polyketides (48.47%), alkaloids (19.21%), steroids and terpenoids (17.03%). Over half of the natural products isolated from Cladosporium have been found to have various biological activities, including cytotoxic, antibacterial, antiviral, antifungal and enzyme-inhibitory activities. These findings testify to the tremendous potential of Cladosporium, especially the marine-derived Cladosporium, to yield novel bioactive natural products, providing a structural foundation for the development of new drugs.

A fluorescent electrophile for CLIPS: self indicating TrkB binders

Combination of cysteine-containing peptides with electrophiles provides efficient access to cyclo-organopeptides. However, there are no routes to intrinsically fluorescent cyclo-organopeptides containing robust, brilliant fluorophores emitting at wavelengths longer than cellular autofluorescence. We show such fluorescent cyclo-organopeptides can be made via SNAr reactions of cysteine-containing peptides with a BODIPY system. Seven compounds of this type were prepared to test as probes; six contained peptide sequences corresponding to loop regions in brain-derived neurotrophic factor and neurotrophic factor 4 (BDNF and NT-4) which bind tropomyocin receptor kinase B (TrkB). Cellular assays in serum-free media indicated two of the six key compounds induced survival of HEK293 cells stably transfected with TrkB whereas a control did not. The two compounds inducing cell survival bound TrkB on those cells (Kd ∼40 and 47 nM), illustrating how intrinsically fluorescent cyclo-organopeptides can be assayed for quantifiable binding to surface receptors in cell membrane environments.

Synthesis of Pyrazole-Based Macrocycles Leads to a Highly Selective Inhibitor for MST3

MST1, MST2, MST3, MST4, and YSK1 are conserved members of the mammalian sterile 20-like serine/threonine (MST) family that regulate cellular functions such as proliferation and migration. The MST3 isozyme plays a role in regulating cell growth and apoptosis, and its dysregulation has been linked to high-grade tumors. To date, there are no isoform-selective inhibitors that could be used for validating the role of MST3 in tumorigenesis. We designed a series of 3-aminopyrazole-based macrocycles based on the structure of a promiscuous inhibitor. By varying the moieties targeting the solvent-exposed region and optimizing the linker, macrocycle JA310 (21c) was synthesized. JA310 exhibited high cellular potency for MST3 (EC50 = 106 nM) and excellent kinome-wide selectivity. The crystal structure of the MST3-JA310 complex provided intriguing insights into the binding mode, which is associated with large-scale structural rearrangements. In summary, JA310 demonstrates the utility of macrocyclization for the design of highly selective inhibitors and presents the first chemical probe for MST3.

Biocatalytic cyclization of small macrolactams by a penicillin-binding protein-type thioesterase

Macrocyclic peptides represent promising scaffolds for chemical tools and potential therapeutics. Synthetic methods for peptide macrocyclization are often hampered by C-terminal epimerization and oligomerization, leading to difficult scalability. While chemical strategies to circumvent this issue exist, they often require specific amino acids to be present in the peptide sequence. Herein, we report the characterization of Ulm16, a peptide cyclase belonging to the penicillin-binding protein-type class of thioesterases that catalyze head-to-tail macrolactamization of nonribosmal peptides. Ulm16 efficiently cyclizes various nonnative peptides ranging from 4 to 6 amino acids with catalytic efficiencies of up to 3 × 106 M-1 s-1. Unlike many previously described homologs, Ulm16 tolerates a variety of C- and N-terminal amino acids. The crystal structure of Ulm16, along with modeling of its substrates and site-directed mutagenesis, allows for rationalization of this wide substrate scope. Overall, Ulm16 represents a promising tool for the biocatalytic production of macrocyclic peptides.

Molecular chameleons in drug discovery

Molecular chameleons possess a flexibility that allows them to dynamically shield or expose polar functionalities in response to the properties of the environment. Although the concept of molecular chameleons was introduced already in 1970, interest in them has grown considerably since the 2010s, when drug discovery has focused to an increased extent on new chemical modalities. Such modalities include cyclic peptides, macrocycles and proteolysis-targeting chimeras, all of which reside in a chemical space far from that of traditional small-molecule drugs. Both cell permeability and aqueous solubility are required for the oral absorption of drugs. Engineering these properties, and potent target binding, into the larger new modalities is a more daunting task than for traditional small-molecule drugs. The ability of chameleons to adapt to different environments may be essential for success. In this Review, we provide both general and theoretical insights into the realm of molecular chameleons. We discuss why chameleons have come into fashion and provide a do-it-yourself toolbox for their design; we then provide a glimpse of how advanced in silico methods can support molecular chameleon design.

Spontaneous and Selective Macrocyclization in Nitroaldol Reaction Systems

Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-β-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.

AAp-MSMD: Amino Acid Preference Mapping on Protein-Protein Interaction Surfaces Using Mixed-Solvent Molecular Dynamics

Peptides have attracted much attention recently owing to their well-balanced properties as drugs against protein-protein interaction (PPI) surfaces. Molecular simulation-based predictions of binding sites and amino acid residues with high affinity to PPI surfaces are expected to accelerate the design of peptide drugs. Mixed-solvent molecular dynamics (MSMD), which adds probe molecules or fragments of functional groups as solutes to the hydration model, detects the binding hotspots and cryptic sites induced by small molecules. The detection results vary depending on the type of probe molecule; thus, they provide important information for drug design. For rational peptide drug design using MSMD, we proposed MSMD with amino acid residue probes, named amino acid probe-based MSMD (AAp-MSMD), to detect hotspots and identify favorable amino acid types on protein surfaces to which peptide drugs bind. We assessed our method in terms of hotspot detection at the amino acid probe level and binding free energy prediction with amino acid probes at the PPI site for the complex structure that formed the PPI. In hotspot detection, the max-spatial probability distribution map (max-PMAP) obtained from AAp-MSMD detected the PPI site, to which each type of amino acid can bind favorably. In the binding free energy prediction using amino acid probes, ΔGFE obtained from AAp-MSMD roughly estimated the experimental binding affinities from the structure-activity relationship. AAp-MSMD, with amino acid probes, provides estimated binding sites and favorable amino acid types at the PPI site of a target protein.

Synthesis of Macrolactams from Macrolactones Using Ru-/Ir-Catalytic System under Neutral Conditions

Herein, we report the Ru-/Ir-catalyzed synthesis of valuable macrolactams from macrolactones and esters. The ring-opening of the macrolactones was efficaciously facilitated by the Ru catalyst to generate 32 amides in the first step. In the second step, intramolecular N-alkylative ring closure of amides with alcohols was succeeded by Ir catalyst to provide a series of 22 macrolactams and gave water as a byproduct. Moreover, this approach proceeded under neutral conditions and avoided the use of external additives.

MicroED as a Powerful Tool for Structure Determination of Macrocyclic Drug Compounds Directly from Their Powder Formulations

Macrocycles are important drug leads with many advantages including the ability to target flat and featureless binding sites as well as to act as molecular chameleons and thereby reach intracellular targets. However, due to their complex structures and inherent flexibility, macrocycles are difficult to study structurally, and there are limited structural data available. Herein, we use the cryo-EM method MicroED to determine the novel atomic structures of several macrocycles that have previously resisted structural determination. We show that structures of similar complexity can now be obtained rapidly from nanograms of material and that different conformations of flexible compounds can be derived from the same experiment. These results will have an impact on contemporary drug discovery as well as natural product exploration.

Stabilized cyclic peptides as modulators of protein-protein interactions: promising strategies and biological evaluation

Protein-protein interactions (PPIs) control many essential biological pathways which are often misregulated in disease. As such, selective PPI modulators are desirable to unravel complex functions of PPIs and thus expand the repertoire of therapeutic targets. However, the large size and relative flatness of PPI interfaces make them challenging molecular targets for conventional drug modalities, rendering most PPIs "undruggable". Therefore, there is a growing need to discover innovative molecules that are able to modulate crucial PPIs. Peptides are ideal candidates to deliver such therapeutics attributed to their ability to closely mimic structural features of protein interfaces. However, their inherently poor proteolysis resistance and cell permeability inevitably hamper their biomedical applications. The introduction of a constraint (i.e., peptide cyclization) to stabilize peptides' secondary structure is a promising strategy to address this problem as witnessed by the rapid development of cyclic peptide drugs in the past two decades. Here, we comprehensively review the recent progress on stabilized cyclic peptides in targeting challenging PPIs. Technological advancements and emerging chemical approaches for stabilizing active peptide conformations are categorized in terms of α-helix stapling, β-hairpin mimetics and macrocyclization. To discover potent and selective ligands, cyclic peptide library technologies were updated based on genetic, biochemical or synthetic methodologies. Moreover, several advances to improve the permeability and oral bioavailability of biologically active cyclic peptides enable the de novo development of cyclic peptide ligands with pharmacological properties. In summary, the development of cyclic peptide-based PPI modulators carries tremendous promise for the next generation of therapeutic agents to target historically "intractable" PPI systems.

A novel cyclic peptide library immobilized on gel-type beads focusing on rapid construction and characterization for comprehensive drug discovery

Medium sized molecules such as peptides and macrocycles have recently drawn much attention as potent sources of medicinal lead compounds, whereas the possibility of obtaining a practical drug from them remains limited. The present paper describes a concept of discovering novel medicinal targets or binding modes as well as lead compounds by the one-peptide-on-one-bead (OPOB) technology for comprehensive screening. The difficulty and problems in conventional drug discovery methods that generally deal with one predetermined target are considered. The building blocks used for the present libraries were selected based on previous results in development of peptidic drugs. Each constituent has the common structure of cyclic form prepared by disulfide of cysteinyl residues or thioether linkages, additionally a methionine residue was inserted for the site-specific rapid cleavage by cyanogen bromide to liberate the immobilized peptides allowing reliable characterization by MALDI-TOF-MS/MS without LC-purification. Thus, a high throughput construction method for cyclic peptide libraries as well as characterization of single bead are proposed for drug discovery.

Addressing Challenges of Macrocyclic Conformational Sampling in Polar and Apolar Solvents: Lessons for Chameleonicity

We evaluated a workflow to reliably sample the conformational space of a set of 47 peptidic macrocycles. Starting from SMILES strings, we use accelerated molecular dynamics simulations to overcome high energy barriers, in particular, the cis-trans isomerization of peptide bonds. We find that our approach performs very well in polar solvents like water and dimethyl sulfoxide. Interestingly, the protonation state of a secondary amine in the ring only slightly influences the conformational ensembles of our test systems. For several of the macrocycles, determining the conformational distribution in chloroform turns out to be considerably more challenging. Especially, the choice of partial charges crucially influences the ensembles in chloroform. We address these challenges by modifying initial structures and the choice of partial charges. Our results suggest that special care has to be taken to understand the configurational distribution in apolar solvents, which is a key step toward a reliable prediction of membrane permeation of macrocycles and their chameleonic properties.

Discovery of Selective and Potent Macrocyclic CDK9 Inhibitors for the Treatment of Osimertinib-Resistant Non-Small-Cell Lung Cancer

Effectiveness of epidermal growth factor receptor (EGFR) inhibitors, including Osimertinib, for treating non-small-cell lung cancer (NSCLC) is limited due to the continuous emergence of drug resistance. Hence, it is urgent to develop new therapeutic approaches. CDK9, a key regulator of RNA transcription, has emerged as a promising target for the development of antitumor drugs due to its crucial role in modulating the levels of antiapoptotic protein Mcl-1. Herein, we present the synthesis, optimization, and evaluation of selective CDK9 inhibitors with a macrocyclic scaffold that effectively suppresses the growth of NSCLC cells. Notably, compound Z11, a potent CDK9 inhibitor (IC50 = 3.20 nM) with good kinase selectivity, significantly inhibits cell proliferation and colony formation and induces apoptosis in Osimertinib-resistant H1975 cells. Furthermore, Z11 demonstrates a significant suppression of tumor growth in six patient-derived organoids, including three organoids resistant to Osimertinib. Overall, Z11 served as a promising macrocycle-based CDK9 inhibitor for treating Osimertinib-resistant NSCLC.